The effect of aging on cellular response to DNA damage was investigated by several approaches. Continuing studies of SCE with aging revealed: 1) spontaneous SCE levels do not change with aging in vivo, 2) that induced SCE levels were not changed in EAT tumor cells implanted in young and old animals, 3) induction of SCE in Chinese hamster cells grown in human serum was influenced by the age of the serum donor. Cloning studies of young and old human cell populations indicated that response to MMC induced DNA damage did not change with aging. Other SCE detection and the use of hepatic cell lines for detecting SCE induction by agents which require metabolic activation.